Manhattanhenge! A skyscraper sunset stops traffic in New York City

New Yorkers were wowed on Wednesday by a sunset that was perfectly framed by skyscrapers, thanks to an urban astronomical phenomenon known as Manhattanhenge.

The same planetary tilt that determines the seasons also dictates exactly where the sun will go down each evening — and because of the way that Manhattan's dominant street grid is laid out, killer sunsets are potentially visible from some of the borough's best-known east-west streets in late May and mid-July.

Tuesday's ceremony was rained out, but the skies were clear enough on Wednesday to make for some beautiful postings on photo-sharing sites such as Instagram and Twitter, Flickr and Facebook.

The traffic issue is of growing concern to Neil deGrasse Tyson, the director of New York's Hayden Planetarium. Tyson is the guy who threw the celestial spotlight on Manhattanhenge more than a decade ago, in a magazine article that was accompanied by his glittering sunset photo.

"Back then, it was just kind of a curiosity, but now it's becoming an annual tradition," Tyson told NBC News. "It started out with tens of people, and then hundreds, and now there are thousands of people who block traffic. I've alerted the police department of this, just as an issue of public safety, that perhaps they should close off streets. We're still trying to resolve that. They're not accustomed to closing off streets for cosmic reasons."

Why is Manhattanhenge such a big deal for New Yorkers? One reason may be that urban residents are starved for cosmic wonders. "They may not receive much of the universe, but when they can, they reach for it. And that's what's going on tonight, and of course for the next one in July," Tyson said Wednesday.

Check out Tyson's guide to Manhattanhenge for more background and a rundown of the times for July's Manhattanhenge events (8:23 p.m. ET on July 12 and 8:24 p.m. ET on July 13). He says the best streets for sun-watching are 14th, 23rd, 34th, 42nd, 57th and several streets adjacent to them. Did you snap some great Manhattanhenge pictures? Share them on the NBC News Science Facebook page, and stay tuned for more in July.